Materials for use for rainwear are known which have a layer of expanded microporous polytetrafluoroethylene (ePTFE) or porous polypropylene, see for example, Gore, et al., U.S. Pat. Nos. 4,194,041 or Henn, 4,969,998. Expanded microporous water-repellent polytetrafluoroethylene material described in Gore, U.S. Pat. No. 3,953,566 is especially well suited for this purpose. It is liquid water repelling, but allows water vapor, in the form of perspiration, to pass through. Polyurethanes and other polymers have been used for this purpose also. To confer good flexibility on the materials for use in the textile sector, the microporous layer should be made as thin as possible. However, a thinner membrane will generally mean a loss of performance, and thin coatings run the risk of decreasing water repellency.
U.S. Pat. No. 4,194,041 describes the use of an additional coating on microporous polymers which is based on a thin, air-impermeable coating composed of a polyetherpolyurethane or polyperfluorosulfonic acid that transports water vapor molecules by diffusion. The thin coating is employed to reduce transmission of surface active agents and contaminating substances through the polymers. Owing to the chemical structure of the polymer, this monolithic coating on the microporous structure exhibits a high transport of water molecules, (high permeability to water vapor) through the polymeric material. This film should be applied as thinly as possible in order not to affect the flexibility, yet confer adequate protection on the composite. Furthermore, water vapor permeability deteriorates greatly in the case of thicker, monolithic films.
Other coatings for microporous materials are described in the art. For example, EP 0581168 (Mitsubishi) describes the use of fluorinated alkyl methacrylate and fluorinated alkyl acrylate for polyolefin membranes. The substances are physically bound to the polymer matrix and contain a crosslinking monomer. The substance is applied in the form of a solution usually in fluorinated solvents. After coating, the solvent is removed. The situation is similar with a process for treating polymers with solutions of amorphous fluoropolymers (WO 92/10532).
Solutions of fluorine-containing polymers are also involved in a patent for coating ePTFE with Teflon AF (EP 0561875). WO 91/01791 (Gelman Sciences Technology; EP 0561277 (Millipore)/U.S. Pat. No. 5,217,802 propose treating a porous membrane with a fluorine-containing monomer and a crosslinker. The treatment is followed by polymerization. Perfluoropolyethers in conjunction with ePTFE for use as water-repellent finish are mentioned in WO 92/21715.
For improved water repellency performance, oleophobicized and hydrophobicized textile substrates sprayed with fluorocarbon emulsions are mentioned in EP 0594154.
A type of composite membrane is known from U.S. Pat. No. 4,969,998. In this membrane the material of the inner layer has in part penetrated into the pores of the microporous outer layer. As the material for the microporous outer layer, microporous expanded polytetrafluoroethylene, is proposed. As for the inner layer a polyether-polythioether is proposed. The latter material up to a certain degree fills the pores of the microporous layer, but is consistently tight, amorphous and nonporous. It is reported that this composite has moisture vapor transmission rates which are higher than the moisture vapor transmission rates of the laminate described first. However, when the composite was used as a textile laminate for rainwear it was found that under extreme athletic load and the associated heavy formation of perspiration, the latter cannot always be dissipated to the environment without residue. The liquid perspiration remaining on the inside of the clothing adversely affects the feeling of well-being and comfort of wearing.